158 The American Geolor/iat. March, 1895 
Paleozoic y,-eology, is the proi'ouud structural change which 
here takes place, and the necessity of recognizing it as the 
base of the Taconic or Lower Cambrian sediments. 
If we inciuire, now, more closely ns to the nature of the lower 
portion of the Taconic, we find everywhere, as already stated, 
a conglomerate at the base. This is true whether we examine 
the (Cambrian's contact with the Archean near the horizon of 
the Olenellus zone, or near the horizon of the Upper Cambrian 
(Olenus zone of Kngland). From this conglomerate upward 
the fragments become finer and finer, making a quartzyte. 
This is followed by a calcareous zone and iron ore, and these 
by black slates. All of these separate })arts ma^^ be seen in 
(contact on the Archean, in different places. 
The unfortunate controversy which arose respecting the age 
of these rocks in America, while not exactly the parallel of 
that which sprang up in Britain between Murchison and Sedg- 
wick over the limits of their respective "sj^stems," has served 
to obscure the actual facts and to prejudice the cause of geo- 
logical research on these most interesting formations. Facts 
which have entered into history, as to this controversy in 
America, need not be revived. But new men, and new issues 
have appeared on all sides, and, as in Britain, much more is 
known now than formerly, of the whole question. So many 
lights have been recently turned on these problems from dif- 
ferent (piarters that nearly all the old problems are solved, and 
the advancing research now has to do with many new prob- 
lems of more direct and special import and more limited 
scope. Only so man}^ of the results of past research will here 
be mentioned as seem to l)ear on the nature of the base of the 
Taconic. 
The following arrangement of the main parts, in descending 
order, seems to be the result of all the work on the Taconic 
strata in the original Taconic area : 
1, A S(>ri('S of slates and schists, often hhick. but soiiieliines i^ruy and 
siliceous; lowiird tlie south beconiini:- roolinu' slates and even mica 
schists. 
2. A iireeiiish, suft. nia.uiiesian schist or shile, sdinet inn-s siliceous, lie- 
cominii' nacreous schist. 
:;. biineslone. iiassinu' to ni;irl>le. associatiMl with (luarl/yte and alter 
nal ions ot mica schist. 
4. (^uart/yte, with alternations of mica schist. 
